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1.
Progress on deep circulation and meridional overturning circulation in the South China Sea 总被引：2，自引：0，他引：2
DongXiao Wang JinGen Xiao YeQiang Shu Qiang Xie Ju Chen Qiang Wang 《中国科学:地球科学(英文版)》2016,59(9):1827-1833
The deep overflow through the Luzon Strait drives the cyclonic deep circulation in the South China Sea (SCS). In the mean time, the intruding Pacific deep water transforms and upwells due to enhanced diapycnal mixing in the SCS. Both processes greatly contribute to the SCS meridional overturning circulation (SCSMOC). At the same time, both the deep circulation and meridional overturning circulation are modulated by rough topography in the SCS. Furthermore, the spatial structure of the SCSMOC infers a link between the upper-layer circulation and deep circulation in the SCS. This paper reviews recent advances in the SCS deep circulation and meridional overturning circulation, including the driving mechanism of the SCS deep circulation and its modulation by topography, as well as the spatial structure of the SCSMOC and its dynamical mechanism. 相似文献
2.
Kyoko Ohashi Jinyu Sheng Keith R. Thompson Charles G. Hannah Harold Ritchie 《Continental Shelf Research》2009
A numerical shelf circulation model was developed for the Scotian Shelf, using a nested-grid setup consisting of a three-dimensional baroclinic inner model embedded inside a two-dimensional barotropic outer model. The shelf circulation model is based on the Princeton Ocean Model and driven by three-hourly atmospheric forcing provided by a numerical weather forecast model and by tidal forcing specified at the inner model's open boundaries based on pre-calculated tidal harmonic constants. The outer model simulates the depth-mean circulation forced by wind and atmospheric pressure fields over the northwest Atlantic Ocean with a horizontal resolution of 1/12°. The inner model simulates the three-dimensional circulation over the Gulf of St. Lawrence, the Scotian Shelf, and the adjacent slope with a horizontal resolution of 1/16°. The performance of the shelf circulation model is assessed by comparing model results with oceanographic observations made along the Atlantic coast of Nova Scotia and in the vicinity of Sable Island (on the Scotian Shelf) during two periods: October 2000–March 2001 and April–June 2002. Analysis of model results on Sable Island Bank indicates that tidal currents account for as much as ∼80% of the total variance of near-bottom currents, and currents driven by local winds account for ∼30% of the variance of the non-tidal near-bottom currents. Shelf waves generated remotely by winds and propagating into the region also play an important role in the near-bottom circulation on the bank. 相似文献
3.
《Continental Shelf Research》1999,19(14):1809-1831
The central Norwegian shelf between 62 and 68°N covers an area of about 150 000 km2. The bottom topography is complicated and consists of several shallow banks separated by deeper channels. The area plays an important site-specific role for the recruitment strategy of the Norwegian spring spawning herring. The aim of this contribution is to elucidate the general circulation pattern and the physical processes related to drift and spreading of herring larvae, primarily by the use of satellite-tracked drifting buoys. The results indicate two drift routes; the main inner one on the coastal side of the banks, and a secondary outer one which follows the shelf break. Both routes are highly governed by the bottom topography. The inner transport route is the proper Norwegian Coastal Current characterised by having the higher drift speeds, the lower mean residence time and the higher current directional stability. Several banks at the shelf may induce topographically trapped eddies. The herring seems to prefer to spawn in these eddies. 相似文献
4.
5.
Simulating the three-dimensional circulation and hydrography of Halifax Harbour using a multi-nested coastal ocean circulation model 总被引：2，自引：2，他引：0
Shiliang Shan Jinyu Sheng Keith Richard Thompson David Alexander Greenberg 《Ocean Dynamics》2011,61(7):951-976
Halifax Harbour is located on the Atlantic coast of Nova Scotia, Canada. It is one of the world’s largest, ice-free natural
harbours and of great economic importance to the region. A good understanding of the physical processes controlling tides,
flooding, transport and dispersion, and hydrographic variability is required for pollution control and sustainable development
of the Harbour. For the first time, a multi-nested, finite difference coastal ocean circulation model is used to reconstruct
the three-dimensional circulation and hydrography of the Harbour and its variability on timescales of hours to months for
2006. The model is driven by tides, wind and sea level pressure, air-sea fluxes of heat, and terrestrial buoyancy fluxes associated
with river and sewage discharge. The predictive skill of the model is assessed by comparing the model simulations with independent
observations of sea level from coastal tide gauges and currents from moored instruments. The simulated hydrography is also
compared against a new monthly climatology created from all available temperature and salinity observations made in the Harbour
over the last century. It is shown that the model can reproduce accurately the main features of the observed tides and storm
surge, seasonal mean circulation and hydrography, and wind driven variations. The model is next used to examine the main physical
processes controlling the circulation and hydrography of the Harbour. It is shown that non-linear interaction between tidal
currents and complex topography occurs over the Narrows. The overall circulation can be characterized as a two-layer estuarine
circulation with seaward flow in the thin upper layer and landward flow in the broad lower layer. An important component of
this estuarine circulation is a relatively strong, vertically sheared jet situated over a narrow sill connecting the inner
Harbour to the deep and relatively quiescent Bedford Basin. Local wind driven variability is strongest in winter as expected
but it is also shown that a significant part of the temperature and salinity variability is driven by physical processes occurring
on the adjacent inner continental shelf, especially during storm and coastal upwelling events. 相似文献
6.
7.
Rationalized by the observational circulation pattern in the upper ocean of the North Pacific, meridional friction term is
first incorporated in a barotropic theoretical model of the wind-driven circulation. The governing potential vorticity equation
thence has β term and wind stress curl term (the two of the Sverdrup balance), zonal friction term and meridional friction
term. The analytical solution satisfactorily captures many important features of the wind-driven circulation in the North
Pacific: Kuroshio, Oyashio, Kuroshio extension, North Equatorial Current, and especially the eastern boundary currents in
the North Pacific, i.e. California current and Alaska current. 相似文献
8.
Charitha Pattiaratchi Dale Olsson Yasha Hetzel Ryan Lowe 《Continental Shelf Research》2009,29(16):1961-1974
Surf zone drifters and a current meter were used to study the nearshore circulation patterns in the lee of groynes at Cottesloe Beach and City Beach in Western Australia. The circulation patterns revealed that a persistent re-circulation cell was present in the lee of the groyne which was driven by changes in wave set-up resulting from lower wave heights in the lee of the groyne. The re-circulation consisted of a longshore current directed towards the groyne which was deflected offshore due to groyne resulting in a rip current along the groyne face. The offshore-flowing rip current and the incoming waves converged at the offshore extent of this circulation cell, with the deflection of the rip current parallel to the shoreline and then completing the recirculation through an onshore component. The Eulerian measurements revealed that 55% of the currents on the lee side of the groyne were directed offshore and that these currents had a maximum speed of 2 m s?1. Spectral analysis of the wave heights and the currents revealed several corresponding peaks in the measured spectral densities with timescales between 12 s and 50 min. Numerical simulations of an idealised beach with a shore-normal groyne were conducted using a circulation model driven by waves, and confirmed the formation of a persistent eddy in the lee of the groyne. Sensitivity studies indicated that the incident wave angle, wave period, and especially the wave height controlled the circulation. The eddy vorticity, a measure of an eddy's strength, increased roughly proportional to an increase in the incident wave energy flux. 相似文献
9.
D. James Baker Jr. 《地球物理与天体物理流体动力学》2013,107(1):17-29
Abstract A two gyre circulation and inertial western boundary currents have been observed in a sloping bottom laboratory model of a barotropic ocean circulation. Water of viscosity v is contained in a rotating (angular velocity ω), square basin of side L (30 cm) with a flat top and a bottom slope (tan θ) such that the depth (H) varies from 12 to 15 cm. The flow is driven by a distributed source and sink at the upper surface, a plate drilled with 342 holes. The hole distribution and size is arranged so that the average imposed vertical velocity, w = w 0 sin (2πy′/30), models the Ekman divergence from a two gyre zonal wind stress. Fluid flow is observed with the thymol blue technique over the ranges of Rossby numbers (w 0/2ωL tan θ) from 1.44 × 10?3 to 1.41 × 10?2 and Ekman numbers (v/2ωH 2) from 2.13 × 10?5 to 2.10 × 10?3. At the largest Rossby numbers the flow pattern changes markedly, but the non-uniformity of the imposed vertical velocity also penetrates deep into the fluid in this regime. 相似文献
10.
Andreas Schiller 《Continental Shelf Research》2011,31(10):1087-1095
The ocean circulation on Australia's Northern Shelf is dominated by the Monsoon and influenced by large-scale interannual variability. These driving forces exert an ocean circulation that influences the deep Timor Sea Passage of the Indonesian Throughflow, the circulation on the Timor and Arafura Shelves and, further downstream, the Leeuwin Current. Seasonal maxima of northeastward (southwestward) volume transports on the shelf are almost symmetric and exceed 106 m3/s in February (June). The associated seasonal cycle of vertical upwelling from June to August south of 8.5°S and between 124°E and 137.5°E exceeds 1.5×106 m3/s across 40 m depth. During El Niño events, combined anomalies from the seasonal means of high regional wind stresses and low inter-ocean pressure gradients double the northeastward volume transport on the North Australian Shelf to 1.5×106 m3/s which accounts for 20% of the total depth-integrated transport across 124°E and reduce the total transport of the Indonesian Throughflow. Variability of heat content on the shelf is largely determined by Pacific and Indian Ocean equatorial wind stress anomalies with some contribution from local wind stress forcing. 相似文献
11.
L. L. Kitchatinov 《Geomagnetism and Aeronomy》2016,56(8):945-951
Mean-field hydrodynamics advanced to clear explanations for the origin and properties of the global meridional flow in stellar convection zones. Qualitative arguments and analysis of basic equations both show that the meridional circulation is driven by non-conservative centrifugal and buoyancy forces and results from a slight disbalance between these two drivers. The deviations from the thermal wind balance are relatively large near the boundaries of convection zones. Accordingly, the meridional flow attains its largest velocities in the boundary layers and decreases inside the convection zone. This picture, however, is neither supported nor dismissed by the conflicting results of recent helioseismic soundings or 3D numerical experiments. The relevant physics of the differential temperature and its possible relation to the solar oblateness are briefly discussed. 相似文献
12.
观测事实揭示,春季Hadley环流在年际时间尺度上与东亚夏季风环流和降水具有密切联系.在未来全球变暖背景下,春季Hadley环流与东亚夏季风环流和降水的这种年际关系是否会发生变化？针对该问题,本文在评估的基础上选取五个气候模式,分析了A1B排放情景下春季北半球Hadley环流年际变率的未来变化及其与东亚夏季风环流和降水的年际关系.多模式集合(MME)预估结果表明,在全球变暖背景下,与20世纪末期(1970—1999年)相比,到21世纪末期(2070—2099年),春季北半球Hadley环流的年际变率强度将减弱,减弱幅度达32%.随着春季Hadley环流年际变率的减弱,其与夏季西太平洋副热带高压和东亚夏季风强度的联系将变弱.MME模拟结果还显示,春季Hadley环流与夏季东亚西风急流和降水的关系也降低,但各单个模式间存在较大差异. 相似文献
13.
Joseph Egger 《地球物理与天体物理流体动力学》2013,107(1-4):75-90
Abstract The south-easterly surface flow down the slopes of Antarctica induces a transfer of westerly angular momentum to the atmosphere, which must be removed from the Antarctic domain by atmospheric transports. It is suggested that synoptic eddies protruding from the northern baroclinic zone into the polar regions are modified by the topography such that they are able to perform these meridional transports. A simple linear two-layer model of the axisymmetric circulation of Antarctica is presented where the eddy effects are incorporated via a K-ansatz. It is shown that qualitatively realistic mean flow patterns can be obtained with this model. The limitations of this approach are exposed. 相似文献
14.
The Pearl River Estuary (PRE) in South China's Guangdong Province is a subtropical estuary with highly irregular topography
and dynamically complicated circulations. A nested-grid coastal circulation modelling system is used in this study to examine
dynamic responses of the PRE to tides, meteorological forcing and buoyancy forcing. The nested-grid modelling system is based
on the Princeton Ocean Model and consists of three downscaling subcomponents: including an outer-most model with a coarse
horizontal resolution of ~7 km for simulating tidally forced and wind-driven surface elevations and depth-mean currents over
the China Seas from Bohai Sea to the northern South China Sea and an innermost model with a fine resolution of ~1.2 km for
simulating the 3D coastal circulation and hydrography over the PRE and adjacent coastal waters. Model results during the winter
northeast monsoon surge in January and super typhoon Koryn in June of 1993 are used to demonstrate that the 3D coastal circulation
and hydrographic distributions in the PRE are affected by tides, winds and buoyancy forcing associated with river discharge
from the Pearl River with significant seasonal and synoptic variabilities. 相似文献
15.
Abstract A nonlinear Stommel model of the ocean circulation on the beta plane, driven by a time periodic wind stress, is investigated in order to study symmetry properties of the observed time-mean ocean gyres. Due to the presence of vorticity advection terms the model will have a steady or rectified response to fluctuating wind fields. In this paper a small inverse Ekman number, “the small beta regime”, is considered. It is demonstrated that for this case all qualitative features of the residual circulation, obtained numerically by Veronis (1970). are reproduced in an analytical way. They include the dipole character of the gyre, its maximum symmetry breaking around the north-south axis for intermediate Reynolds numbers, measuring the ratio of vorticity forcing and dissipation, and the maximum residual response for intermediate forcing frequencies. 相似文献
16.
Roberto Fioravanti Carelli Fontes Belmiro Mendes Castro Robert C. Beardsley 《Ocean Dynamics》2008,58(3-4):187-198
We studied the circulation on the coastal domain of the Amazon Shelf by applying the hydrodynamic module of the estuarine and coastal ocean model and sediment transport. The first barotropic experiment aimed to explain the major bathymetric effects on tides and those generated by anisotropy in sediment distribution. We analyzed the continental shelf response of barotropic tides under realistic bottom stress parametrization (C d ), considering sediment granulometry obtained from a faciologic map, where river mud deposits and reworked sediments areas are well distinguished, among others classes of sediments. Very low C d values were set in the fluid mud regions off the Amapá coast (1.0 10???4), in contrast to values around 3.5 10???3 for coarser sediment regions off the Pará coast. Three-dimensional experiments represented the Amazon River discharge and trade winds, combined to barotropic tide influences and induced vertical mixing. The quasiresonant response of the Amazon Shelf to the M2 tide acts on the local hydrodynamics by increasing tidal admittance, along with tidal forcing at the shelf break and extensive fluid mud regions. Harmonic analysis of modeled currents agreed well with the analysis of the AMASSEDS observational data set. Tidal-induced vertical shear provided strong homogenization of threshold waters, which are subject to a kind of hydraulic control due to the topographic steepness. Ahead of the hydraulic jump, the low-salinity plume is disconnected from the bottom and acquires negative vorticity, turning southeastward. Tides act as a generator mechanism and topography, via hydraulic control, acts as a maintainer mechanism for the low-salinity frontal zone positioning. Tidally induced southeastward plume fate is overwhelmed by northwestward trade winds so that they, along with background circulation, probably play the most important role on the plume fate and variability over the Amazon Shelf. 相似文献
17.
Fred Ward 《Pure and Applied Geophysics》1964,58(1):157-186
Summary One of the main results of the rotating cylinder experiments ofFultz andHide is that the general flow regime in them is essentially determined by the ratio of the angular velocity of the fluid motions (relative to the cylinder) to that of the cylinder itself. Extending these results to the atmosphere of the sun, leads to the hypothesis that the layer in which spots are imbedded should exhibit a non-axially symmetric pattern, of theRossby type.The fluid motions, characteristic of such a general circulation pattern, are mainly along spherical surfaces, and have a wavelike (eddy) appearance similar to the planetary waves in the upper troposphere of the terrestrial atmosphere. These eddies transport momentum along these spherical surfaces from regions of relatively lower angular velocity to regions of higher velocity. Tracers (e.g., sunspots) imbedded is such a flow would show a correlation between their proper motions in latitude and longitude, such that spots moving equatorward will tend to have larger longitudinal motions (toward the west limb), and vice versa.Analysis of ten years (1935 to 1944) of Greenwich spot data shows a consistent, and (statistically) very significant correlation of spot group proper motions, in the proper sense. These results provide strong support for the existence of large-scale waves which are some modest fraction of the solar circumference, but larger than the sunspot groups. Moreover, these waves transport angular momentum (up the gradient of angular velocity) toward the equatorial regions from higher latitudes across at least the entire sunspot zone. It is not known, however, whether these eddies are the primary (or only) source of momentum to maintain the equatorial acceleration of the sun. However, if this source were shut off, and all other processes continued unabated, this layer of the sun between latitudes ±20° would reach solid rotation in about 51/2 rotations.Because this eddy transport of momentum is counter to the gradient of angular velocity, there is an implied transformation of the kinetic energy of the eddies into the kinetic energy of the mean east-west flow. Of possibly even more interest, however, might be the possibility of transfers of kinetic energy between eddies of all different scale sizes extending down the entire spectrum to include sunspot groups and the spots themselves. Moreover, some eddy size(s) in this layer is likely to be primarily responsible for a conversion of potential to kinetic energy.A result of subsidiary interest is the systematically higher value of solar rotation (at all latitudes) derivable from this data, which includes all spots which survive for at least two days. In contrast to the work of previous authors who used only long-lived spots, the result obtained when many small spots are used, indicates perhaps a variation of the rotation rate with height in the solar atmosphere.The results provide no evidence to indicate the existence of significant meridional circulations (latitudinal driffs). 相似文献
18.
Measurements from recently installed 5 MHz high-frequency radar (CODAR) stations south of Point Arena, California, are used to describe surface current patterns during the upwelling season (June-August 2007). The systems provide hourly current maps on a 5-km grid, covering a region from approximately 10 to 150 km offshore (the continental shelf into the deep ocean). These HF-radar observations provide an unprecedented view of circulation in this “coastal transition zone”, between the wind-driven circulation over the shelf and the California Current circulation offshore. Circulation patterns include: (1) bifurcation of the coastal upwelling jet downstream of Point Arena into an along-shelf (down-coast) branch and an offshore branch, and (2) a large-scale anticyclonic meander that often develops into an eddy-like recirculation south of the bifurcation. The “recirculation” feature extends well offshore, with surface currents 50-100 km from the coast consistently opposing the wind stress. The spatial and temporal evolution of the surface current features during upwelling events affects surface transport from Point Arena to areas in the south, increasing the travel time of a substantial fraction of newly upwelled water from a few days to roughly two weeks. Thus, surface currents even far offshore influence coastal transport of nutrients, phytoplankton and larvae on ecologically relevant timescales, with resultant connectivity patterns very different than implied by a simple examination of the mean flow. 相似文献
19.
This study examines main physical processes affecting the three-dimensional (3D) circulation and hydrographic distributions over the inner Scotian Shelf (ISS) in June and July 2006 using a nested-grid coastal ocean circulation modeling system known as the NCOPS-LB. The nested-grid system has five relocatable downscaling submodels, with the outermost submodel of a coarse horizontal resolution of (1/12)° for simulating storm surges and barotropic shelf waves over the Eastern Canadian shelf and the innermost submodel of a fine resolution of ～180 m for simulating the 3D coastal circulation and hydrography over Lunenburg Bay of Nova Scotia in the default setup. The NCOPS-LB is driven by meteorological and astronomical forcing and used to study the storm-induced circulation over the ISS during tropical storm Alberto. Model results demonstrate that the coastal circulation and hydrographic distributions over the ISS are affected significantly by tides, local wind forcing, and remotely generated coastal waves during the study period. 相似文献
20.
Some aspects of the monsoon circulation and monsoon rainfall 总被引：1，自引：0，他引：1
R. Ananthakrishnan 《Pure and Applied Geophysics》1977,115(5-6):1209-1249
Summary The south Asian summer monsoon from June to September accounts for the greater part of the annual rainfall over most of India and southeast Asia. The evolution of the summer and winter monsoon circulations over India is examined on the basis of the surface and upper air data of stations across India. The salient features of the seasonal reversals of temperature and pressure gradients and winds and the seasonal and synoptic fluctuations of atmospheric humidity are discussed. The space-time variations of rainfall are considered with the help of climatic pentad rainfall charts and diagrams. The rainfall of several north and central Indian stations shows a minimum around mid-August and a maximum around mid-February which seem to be connected with the extreme summer and winter positions of the ITCZ and the associated north-south shifts in the seasonal circulation patterns. Attention is drawn to the characteristic features of the monsoon rainfall that emerge from a study of daily and hourly rainfall of selected stations. Diurnal variations of temperature, pressure, wind and rainfall over the monsoon belt are briefly treated. 相似文献